1. Field of the Invention
The invention relates to a light source, and more particularly to a backlight module.
2. Description of Related Art
With rapid progress in display techniques, the flat panel display has become the mainstream among various displays and replaced the cathode ray tube (CRT). Among various flat panel displays, the liquid crystal display (LCD) has been deeply favored by the consumers for usage. The LCD includes a liquid crystal panel and a backlight module. The LCD does not luminesce by itself, but is used to determine a light passing rate. Thus, a backlight module is disposed behind the liquid crystal panel as a surface light source of the same. The optical quality of the surface light source greatly affects the display quality of the LCD. For example, in order to enhance the brightness of the display image, the range of a light emitting angle of the surface light source has to be smaller.
In a conventional side-type backlight module, a bottom diffusion sheet, two prism sheets having prism columns interlacing each other, and a top diffusion sheet are disposed from the bottom to the top sequentially. The prism sheets are configured to reduce the range of the light emitting angle, and the top diffusion sheet and the bottom diffusion sheet are configured to uniform the light and prevent the contours of the prism columns and the liquid crystal panel from generating moiré with the LCD. However, the method of disposing four optical films on top of the light guide plate increases the cost of the backlight module. Also, too many optical films lead to assembly difficulty and poor reduction in thickness of the backlight module. Also, the adoption of up to four optical films causes light loss easily, so that the positive brightness of the backlight module is difficult to be further enhanced.
In U.S. Pat. No. 6,091,547, two light emitting control films each having a plurality of trigonal prisms is disclosed. In U.S. Patent Publication No. 20080043172, a backlight module having a light source, a first prism sheet, a second prism sheet, and a light guide plate is disclosed. The publication, entitled “the application of anisotropic silicon etching and electroforming to the fabrication of brightness enhancement films”, with a reference number of D-17-0024 in the 24th National Conference on Mechanical Engineering of The Chinese Society of Mechanical Engineering disclosed a fabrication method of an optical brightness enhancement film and an optical feature thereof.